Photoelectric conversion films have been widely used in, for example, optical sensors. In particular, they are appropriately employed as solid-state imaging elements (photoreceptors) in imaging devices (solid-state imaging devices) such as TV cameras. Concerning materials of photoelectric conversion films to be used as solid-state imaging elements in imaging devices, films made of inorganic materials such as Si films and a-Se films are mainly employed.
Conventional photoelectric conversion films with the use of these films made of inorganic materials have no sharp wavelength-dependency in the photoelectric conversion properties thereof In imaging devices with the use of photoelectric conversion films, therefore, it has been a main practice to employ a three sheet structure which comprises a prism for dividing incident light into the three primary colors (i.e., red, green and blue) and three photoelectric conversion films provided in the latter part of the prism.
However, it is unavoidable that such an imaging device of the three sheet-structure has a large size and a large weight because of its structure.
To reduce the size and weight of an imaging device, it is desirable to employ a single sheet structure comprising a single photoreceptor alone without a need for forming an optical prism. For example, studies have been made to construct an imaging device having a single sheet photoreceptor provided with red, green and blue filters. Also, studies have been made to use organic materials which are advantageous in, for example, having a large degree of freedom in shape processing. JP-A-2003-158254 reports a photoelectric conversion film having an elevated photosensitivity (sensitivity) and a photoreceptor using the same. Although organic materials are employed as a p-type semiconductor and an n-type semiconductor in this document, nothing but a case wherein polymethylphenylsilane (PMPS) was employed as the p-type semiconductor while 8-hydroxyquinoline aluminum complex (Alq3) as the n-type semiconductor and coumarin 6 was added as an organic dye in an amount of 5.0 parts by mass per 100 parts by mass of PMPS is reported in EXAMPLES of this document. In the description of preferred embodiments in this document, moreover, it is merely stated that an organic dye is preferably used in an amount of from 0.1 to 50 parts by mass per 100 parts by mass of the p-type or n-type semiconductor constituting the photoelectric conversion film. That is, it is not described therein to employ an organic dye as a p-type or n-type semiconductor.
To reduce the size and weight of an imaging device, JP-A-2003-234460 proposes a laminated photoelectric conversion film having a low resolution as a photoelectric conversion film of a single sheet structure comprising a single photoreceptor alone without a need for forming an optical prism. According to this document, it is pointed out that a preferable photoelectric conversion film of the lamination type comprises, for example, a photoelectric conversion film capable of absorbing light of the wavelength of one of the three primary colors, another photoelectric conversion film capable of absorbing the wavelength of another color, and still another photoelectric conversion film capable of absorbing the wavelength of the remaining color which are laminated each other so as to give a color image having a high sensitivity and a high resolution.
However, EXAMPLES of this document merely present a photoelectric conversion film in which a coumarin 6/polysilane film having a photosensitivity over the whole blue color region of 500 nm or below and a ZnPc/Alq3 film having an absorption range over the red and blue regions are employed as photoelectric conversion films and which shows a photosensitivity exclusively over the almost red color region around 600 to 700 nm due to the filtering effect of the coumarin 6/polysilane film.
JP-A-2003-332551 reports a photoconductive film of the lamination type similar to JP-A-2003-234460. However, JP-A-2003-158254, JP-A-2003-234460 and JP-A-2003-332551 refer nothing to the orientation of an organic compound, a J aggregate of an organic dye compound or the angle between the spectral absorption transition dipolar moment of a dye compound and the electrode plane of a photoelectric conversion element, as will be discussed hereinafter.
On the other hand, the orientation of an organic compound can be controlled by appropriately selecting a substrate, controlling vapor deposition conditions, and so on as reported by “Hyomen, 1993, Vol.31(10), p.40”. As an example, a method which comprises rubbing the substrate surface and imparting anisotropy to an organic compound to be grown thereon may be cited.
However, it is observed that a structure depending on substrate crystallization has ten and several layers in thickness at the largest and a film structure shifts toward a bulk crystal structure with an increase in the film thickness. It is preferable that a photoconductive film has a layer thickness of 100 nm or above (i.e., 100 molecular layers or more) to achieve a high light absorptivity. Thus, the proposals in these documents are hardly applicable to photoconductive films. It is considered that, in a photoconductive film, orientation should be controlled with the use of the interaction between organic compound molecules, in addition to the substrate.
J aggregates of an organic dye compound are reported in “The Theory of the Photographic Process, ed. by James, 4th ed., McMillan, 1977, Vo.8, pp.214 to 222”. The term “J aggregate” means an aggregate the absorption of which shifts toward the long wavelength region compared with the absorption of a monomer not interacting among dye molecules. It is generally known that, when a J aggregate is formed, the absorption width in the long wavelength side becomes narrower compared with the monomer state.
With respect to the above element, no specific declaration is made on the green color region. Further, the above document refers neither to a photoelectric conversion element having the bulk heterojunction structure nor to the organic tandem structure.
Although JP-A-2003-332551 reports a photoelectric conversion element of the lamination type similar to JP-A-2003-234460, it refers neither to a photoelectric conversion element having the bulk heterojunction structure nor to the tandem structure.
On the other hand, a photoelectric conversion element having a bulk heterojunction layer as an intermediate layer between pn junction layers is described in “M. Hiramoto, H. Fujiwara, M. Yokoyama, J. Appl. Phys., 1992, Vol.72, p.3781”. In this document, it is a perylene pigment and a phthalocyanine pigment are cited as organic semiconductors. Although it is described therein that this photoelectric conversion element is applicable to a solar cell, nothing is stated about imaging elements.
Although “M. Hiramoto, M. Suezaki, M. Yokoyama, Chem. Lett., 1990, pp.327 to 330” and “A. Yakimov, S. R. Forrest, Appl. Phys. Lett., 2002, Vol.80, pp.1667 to 1669” report the organic tandem structure, they aim at using energy of a solar cell and so on and nothing is stated about imaging elements. Moreover, it is not described therein to apply an electric field between electrodes, etc.